Grid Alignment system problem in BGE
At the moment you have the scale set at 0.01. From the testing I have just done this means you can zoom in so that each grid square that you are trying to snap to is a single micro meter. Do you really need to build roads to that level of accuracy? 



Wouldn’t it be easier to leave the scale at 1.0, then the smallest grid square that can be snapped to is a millimeter?

Which perhaps would mean that you wouldn’t be hitting the rounding / precision issue that Duarte mention ?



Posted this in the Answers section because I can’t add images in Comments